Northstar Engines and System Technical Discussion Discussion, Just a head gasket failure? in Cadillac Engine Technical Discussion; For you guys that have "seen it all," I'd like to hear your opinions. My 2000 DeVille had the classic ...
For you guys that have "seen it all," I'd like to hear your opinions. My 2000 DeVille had the classic symptoms of overheating as many have described on Northstar engines. I just got the heads off of my Northstar. Each head bolt took 90 to 110 ft-lbs of torque to break loose the threads and at least half a turn to unload the bolt. When I examined the head gasket seal around each cylinder, there appeared to be only one leak, located on the front side of cylinder #2, directly into the coolant passage adjacent to the chain drive cavity at the front of the head. There was a similar but less noticeable condition on the front side of cylinder #1, probably just developing.
This engine has had an easy 86k miles put on it and the inside is really clean except for carbon buildup on top of the pistons. This problem appears to be just a gasket failure, not a head bolt thread failure. The threads in the block all look OK, with no significant corrosion or casting porosity. No aluminum came out with the threads. I bought a stud kit, but I'm not convinced that the studs will prevent the head gasket from failing again at the same location.
Is there a particular head gasket that will maintain seal at this location?
Is there a way to o-ring the top of each cylinder as you would do if you were building a blower motor?
Is there some other procedure that will help this problem, such as resurfacing the head to produce a crown down the middle of the head?
Second part: With the engine so far disassembled, it is tempting to put in new piston rings, but I can see the gap in the top ring looks like .015 -.020 inch. That gap indicates that ring wear has been negligible. The crosshatching in the cylinders is still there and there is no wear ring at the top of any cylinder. When you have taken pistons out of engines with similar mileage, how much ring wear have you observed?
Two of my Northstars all developed HG failures without noticeable bolt thread failures. All failed at the #1 cylinder right next to the end of the water jacket. Slightly noticeable on the Seville, and definitely noticeable on the Deville. I repaired them all with studs and new felpro head gaskets. No fancy business other than straight up gasket replacements and bolt hole repair.
On the Seville with 89k, I had no reason to mess with the lower end so I left it alone. The engine had been working perfect with no leaks so I never bothered.
When I pulled my Deville engine out at 110k, the rings were all well within spec so I reused them all. The engine had a severe halfcase leak since years ago, so it's got some new RTV sealants also (the main reason why it was pulled apart into pieces). The only thing that physically broke was the timing chain tensioner which was in terrible shape (it would not keep the tension - will move with the chain movement). I wonder how this made no noise. Anyway, all new timing components.